Picking up where Part 6 left off, we continue to explore prenatal genetic screening. Read on for the visual reason why an ultrasound screening technique was developed for Down syndrome and how the obstetrician pictured above explained why ACOG changed its guidelines so that all women were to be offered prenatal genetic testing for Down syndrome.
A first trimester screen was sought out. So much so, that the National Institutes of Health funded a $10+ million study: the First And Second Trimester Evaluation of Risk or the “FASTER” (get it?) study. In the late 1990’s, Dr. Kypros H. Nicolaides, a Greek maternal-fetal medicine specialist, published a report finding a correlation between the thickness of the fetus’s neck and the incidence for Down syndrome, the thicker the area of the neck measured, the more likely the child had Down syndrome. The area measured was the nuchal fold, also referred to as “nuchal translucency” or “NT”. When the NT measurement was combined with an analysis of certain proteins in the mother’s blood, it approached or exceeded the relative accuracy of the Quad test. And, best of all, for purposes of the FASTER study, the NT-combined screen (as it was termed), was available in the first trimester. Indeed, it was only recommended to be performed between weeks 9 and 11 of gestation.
The reason that NT was even conceived and developed echoed the reason given by the Sequenom representative for diagnostic testing.
In 2013, I attended the annual conference for ACMG, where, by that point, I was no longer just attending or even exhibiting, but presenting, albeit at the lowest echelon of presentations: a poster presentation. Usually tucked at the back of an immense exhibit hall, rows and rows of bulletin boards are arranged like dominoes. Tacked to these boards are “posters,” large printouts, typically around 4ft X 8ft, graphically reporting on the results of some research or study. Standing next to these posters during the assigned times for presenting is one or two of the study’s authors. Conference organizers lure attendees into viewing the posters by placing the hors d’oeuvres stations throughout the rows of posters. As attendees mill about, the poster presenters, in hushed tones, will say to passerbys, “I’m one of the authors, in case you had any questions.” They rarely do, but, I have learned some key insights during these poster presentation sessions.
At the 2013 ACMG conference, during one of the slots for some of the other poster presenters to present, I approached a poster by the laboratory Cellscape. It was reporting on their efforts to find intact fetal cells in the mother’s blood stream, for which, theoretically, a full diagnostic test could be performed. The presenter and I were talking about the advances of prenatal testing, when she said, “Well, you know why NT came about don’t you? It’s because the fetus looks like a person with Down syndrome. Just as most people with Down syndrome have a thicker fold at the base of their neck, so, too, does the fetus.” I was familiar with the common facial characteristics that cause people with Down syndrome to stand out in a crowd. If looking at the right characteristic, they stand out even in the womb.
The combination of the FASTER report on the combined-NT screen and the two published studies showing a lower chance of miscarriage with CVS and amnio, prompted the sea change in prenatal care ushered in by ACOG Practice Bulletins Nos. 77 & 88.
Prior to 2007, the standard of practice was to only offer prenatal testing for Down syndrome (and other genetic conditions) to women 35 or older, termed “advanced maternal age” or “AMA” by the medical guidelines. This age limit was chosen based on the following risk trade-off: the risk of having a miscarriage from diagnostic testing was roughly equivalent to the chance the child would have Down syndrome. As Dr. James Goldberg, a member of ACOG’s guideline committee [pictured above], was quoted in the New York Times’ reporting on the new ACOG guidelines,
losing a normal pregnancy secondary to the [diagnostic] procedure is not as problematic as the birth of a Down syndrome child, so they’re willing to take that risk.
The FASTER study would erase the AMA standard. With ACOG PB 77, now all expectant mothers were to be offered prenatal testing for Down syndrome and other genetic conditions. Due to a first trimester test being available that had an accuracy similar to that of the second trimester QUAD test, and with the miscarriage rate reportedly lower, ACOG decided there no longer were reasons for offering prenatal genetic testing to only high risk women.
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